1. Field of the Invention
The present invention relates to a piezoelectric component and a method of manufacturing the piezoelectric component. In the piezoelectric component, a periphery of a piezoelectric element is covered by an elastic material, and the circumference of the elastic material and the piezoelectric element is covered by an outer-cladding resin.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 1-228310 describes a piezoelectric component in which a periphery of a piezoelectric element having end electrodes connected to lead terminals is covered by an elastic material such as a silicone rubber, and the circumference thereof is sealed by an outer-cladding resin.
In order to manufacture such a piezoelectric component, first, a lead terminal is attached to a piezoelectric element. Then, a silicone rubber layer is provided on the piezoelectric element by the dipping the piezoelectric element in a liquid-state silicone rubber and hardening the rubber layer by applying heat. Further, an epoxy resin layer is provided on the exterior of the silicone rubber via a dipping method. Then, the epoxy resin is hardened by heat to obtain an outer-cladding resin.
The epoxy resin used for forming the outer-cladding resin layer contracts when it is hardened by heat, and thereby a stress caused by the outer-cladding resin which contracts and compresses the interior of the piezoelectric component is generated. If the amount of stress which contracts and compresses the piezoelectric element in the piezoelectric component changes, the oscillation characteristics thereof change. The silicone rubber is used because it is able to prevent the change of the oscillation characteristics of the piezoelectric element, and has a damping effect which suppresses the waveform distortion of the piezoelectric element.
To reduce the stress generated in the piezoelectric element by the outer-cladding resin, preferably, the difference between the edge portion of the piezoelectric element and the outer-cladding resin i.e., the minimum thickness of the silicone rubber, is larger than the contraction amount of the outer-cladding resin when it is hardened, and further, is larger than the difference between the thermal expansions of the outer-cladding resin and of the piezoelectric element.
However, the dipping method for forming the liquid-state silicone rubber was not satisfactory for obtaining a required thickness of the silicone rubber at the end portions of the piezoelectric element, because of the surface tension of the silicone rubber. Therefore, the temperature characteristics of the piezoelectric components are largely varied by the stress generated in the piezoelectric element by the outer-cladding resin.